getbundle: cleanly handle remote abort during getbundle bundle2 allow the server to report error explicitly. This was initially implemented for push but there is not reason to not use it for pull too. This changeset add logic similar to the one in 'unbundle' to the client side of 'getbundle'. That logic make sure the error is properly reported as "remote". This will allow the server side of getbundle to send clean "Abort" message in the next changeset.